The processing and disposal of radioactive and hazardous waste materials is one of the most pressing environmental remediation problems. In most cases, such waste materials have a wide range of compositions that include metals, ceramics, and organic materials. It is generally desirable that prior to disposal, such waste materials are reduced to a compact form. Compaction of the waste materials is typically achieved by melting the waste and cooling the molten mass to crystallized or vitreous (slag) materials.
One approach to the melting and reducing of waste materials is disclosed in U.S. Pat. Nos. 4,770,109 issued Sep. 13, 1988, and 5,136,137 issued Aug. 4, 1992. This approach employs a rotating drum adapted to receive a hot plasma from a plasma torch for melting the mixed waste and discharging the molten mass into an ingot mold. The thus produced and cooled waste products are poured into containers together with the ingot molds for final disposal. Emitted toxic gases given off by the thermal decomposition of organic and hazardous materials are partially incinerated in the reactor vessel, with the remainder further incinerated in a secondary burner and, after transiting an off-gas system, released into the environment. The rotating drum is comprised of a ceramic material which offers only limited heat resistance and corrosion resistance to metals or to the slag molten mass generated during reduction of the waste materials. As a result, the rotating drum must be periodically replaced, which procedure is complicated by the high level of radioactive contamination of the drum. Also in the rotating drum approach, the radioactive materials are spread out throughout the entire volume of the thus produced solid waste product, limiting the compaction of the radioactive waste and requiring the entire product to be handled and disposed of as radioactive waste, substantially increasing the complexity and cost of such disposal.
Currently, the most promising radioactive waste form for handling and disposal involves the incorporation of the radioactive waste into a glasslike matrix of a special composition which is not subject to destruction during long-term storage. It would therefore be highly desirable to be able to separate the radioactive waste material from the nonradioactive waste and to incorporate the radioactive waste into a glasslike matrix having a very durable and stable composition and structure for long-term storage. Prior art approaches do not provide for the separation of radioactive materials from the remaining hazardous waste materials, and do not account for the generation and discharge into the atmosphere of hazardous gases generated during the waste melting process. Thus, toxic gases given off during the high temperature decomposition of organic and toxic materials are discharged from the reactor vessel into the atmosphere.
The present invention addresses the aforementioned limitations of the prior art by providing apparatus and a method for the processing of solid mixed waste which allows for the discharge of a radioactive slag molten mass directly into a waste tank intended for final disposal, while a non-radioactive molten metal mass is crystallized into a compact ingot which could be recycled into radioactive waste storage containers. The present invention allows for the continuous processing of solid mixed waste material over an extended period of time without requiring the replacement of, maintenance to, or cleaning of the reaction vessel. The high temperatures achieved in the reaction vessel convert the toxic gases given off from the decomposition of organic and toxic materials to environmentally safe gases which can be discharged to the atmosphere.